At present, there are mainly capacitive and ultrasonic fingerprint identification devices. They, however, share a common defect that a sensor has a shorter sensing distance, which severely limits the structure and performance of fingerprint identification devices and affects their wide application in mobile terminal products.
An optical fingerprint identification device has the advantage of long-distance sensing. However, since an optical sensor requires high resolution, it can only be made in a small size. Since an optical signal quantity is usually proportional to the area of a sensor, the detected optical signal quantity may be very weak. Therefore, an active detection circuit is usually used for fingerprint identification and detection.